Air kerma is the quantity used to describe which of the following?

Air kerma is the quantity used to describe which of the following?

• A. The energy transferred to air at a point
• B. The energy absorbed by tissue
• C. The dose equivalent
• D. The radioactivity present in air

Answer: (C)

Air kerma describes the kinetic energy transferred from the incident photons to charged particles in air per unit mass at a point. In other words, it is the energy the beam transfers to the air itself at that location, before any of that energy is deposited in tissue or weighed for biological effect. It isn’t the energy absorbed by tissue (that would be absorbed dose), nor the dose equivalent (which accounts for biological effect using weighting factors), nor a measure of radioactivity in the air. To connect kerma to tissue dose you’d apply conversion factors, but the direct quantity described by air kerma is the energy transfer to air at a point.

Air kerma describes the kinetic energy transferred from the incident photons to charged particles in air per unit mass at a point. In other words, it is the energy the beam transfers to the air itself at that location, before any of that energy is deposited in tissue or weighed for biological effect. It isn’t the energy absorbed by tissue (that would be absorbed dose), nor the dose equivalent (which accounts for biological effect using weighting factors), nor a measure of radioactivity in the air. To connect kerma to tissue dose you’d apply conversion factors, but the direct quantity described by air kerma is the energy transfer to air at a point.